1. Field of the Invention
The present invention relates to a display device. More particularly, the present invention relates to a display device including an oxide thin film transistor.
2. Discussion of the Related Art
Flat panel displays (FPDs) include: liquid crystal display device (LCD), a plasma display panel device (PDP), an organic light emitting display device (OLED), and an electrophoretic display device (EPD) and so forth. The FPDs are provided in a relatively thin package that is suitable for use in a variety of electronic goods. As such, FPDs are commonly employed in a wide variety of electronic devices, such as televisions, computers, and handheld devices (e.g., cellular telephones, audio and video players, gaming systems, and so forth). Among the various FPDs, the liquid crystal display device and the organic light emitting display device, which include a thin film transistor, typically use less power than comparable display technologies, making them suitable for use in battery-powered devices or in other contexts where it is desirable to minimize power usage.
The performance of FPDs may be measured with respect to a variety of factors. For example, some characteristics of interest with respect to a FPD may include transmittance (luminance), color accuracy, power efficiency, as well as operating stability. The thin film transistors used in FPD are often closely related to those characteristics of the FPDs. Accordingly, research regarding an oxide thin film transistor for FPDs has been actively conducted.
When fabricating an oxide thin film transistor (TFT) during manufacturing of a display panel, alignment may stray away from the original design of the TFT. The misalignment during the fabrication of the TFT may cause a short channel phenomenon, in which the channel length of the TFT becomes short due to a drain bias.
Drain-induced barrier lowering (DIBL) occurs due to the short channel phenomenon, whereby a threshold voltage Vth of the thin film transistor is shifted in a negative direction. The negative direction indicates a direction toward a negative voltage. For example, the negative voltage may be a voltage less than 0V. In some cases, electrodes and the active layer of the TFT may not be properly aligned in reference to each other, and an unintended current path can be formed by the part of the active layer exposed outside the electrodes (i.e., part of the active layer other than the part between the source and drain, which is intended for providing the channel in the TFT). Current may flow into the exposed area of the active layer, creating an unintended current path in the TFT, known as a side channel, which may shift the threshold voltage of the oxide thin film transistor in the negative direction. As the threshold voltage is shifted in the negative direction, stability of the thin film transistor may be hampered, which in turn reduces the lifetime of the display panel.